The invention relates to a head wheel arrangement of a recorder.
A recording head wheel arrangement with a periodic stroke movement of the head wheel may be necessary for a so-called matrix-type recording. In the matrix-type recording, successive blocks are recorded with recording tracks running approximately parallel to the edge of the tape, as disclosed in a German Offenlegungsschrift (laid open patent application) DE-3509584. A specific embodiment of such head wheel arrangement is described in U.S. Pat. No. 4,774,606 in the name of Dietmar, entitled "HEAD WHEEL ARRANGEMENT FOR A RECORDER WITH THREADED SPINDLE FOR ADJUSTABILITY". In the Dietmar Patent arrangement, a rotating head wheel is mounted, by way of an engaging nut, on a threaded spindle rotating in the same direction. The rotation speed of the spindle varies in accordance with a control voltage to perform the stroke movement.
In such head wheel arrangement, requirements for the precision of the stroke movement are high, especially when the width of each track successively written due to the stroke movement is only 10 to 20 .mu.m. In such head wheel arrangement, in which a rotation movement is turned into a movement of translation using spindle and nut, variations in turning moment may occur. Such variations in the turning moment may occur particularly due to a mechanical over-rigidity. Consequently, inaccuracies may appear in the linear translation movement.
It may be desirable to reduce variations of the turning moment due to the aforementioned mechanical over-rigidity for obtaining a stroke movement with high precision.
In accordance with a feature of the invention, the nut that engages the spindle includes two nuts which are biased by a spring in the axial direction. The spring prevents the nuts from being twisted relative to each other. Advantageously, both nuts are thereby continuously in contact with the respective flanks of the screw threads of the spindle. The result is that there is no more backlash between the nuts and the spindle.
In a preferred embodiment of the invention, one of the nuts is connected with a bush bearing surrounding the circumference of the spindle shaft such that the nuts cannot be moved axially in relation to the bearing in the direction of the axis. However, the nuts are flexible laterally with respect to the axis, i.e. in the radial direction. Consequently, defects in the concentricity of a circumference of the spindle or of the center line of the spindle in an amount of several micro-meters cause a sideways excursion of the nuts without considerably affecting the bearing. It should be understood that defects in the concentricity of the bearing, which is produced on a lathe, may be kept low, using suitable production engineering technique; whereas, defects in concentricity due to the threads of the spindle and of the nuts are considerably larger and more difficult to avoid. By reducing the variations in turning moment per spindle revolution, linear lift movement is obtained. The result is that the control of the linear speed and amplitude of the lift movement is improved.